JPS6014150A - Electronic range - Google Patents

Abstract

PURPOSE:To operate normally an absolute humidity sensor even in a low-temperature state by heating the atmosphere of the absolute humidity sensor with a heating means when the atmospheric temperature is low. CONSTITUTION:A magnetron 6 and a heater 44 are attached to the ceiling part of an oven 5, and food 7 placed on a cooking table 4 is heated by oscillation of the magnetron 6. The inside of the oven 5 is heated by the heater 44. Gas generated by heating food 7 is discharged to the outside through an exhaust passage 9 by a fan 8. An absolute humidity sensor (AH sensor) 10 is attached to the wall of the exhaust passage 9 and detects the humidity of gas passing the exhaust passage 9. Atmospheric temperature of two thermistors constituting the AH sensor are compared with a reference temperature; and if atmospheric temperatures of thermistors are lower than the reference value at a feed start time, the atmosphere of thermistors is heated for a prescribed time to promote self-heating of thermistors.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a microwave oven equipped with an absolute humidity detection device;
In particular, the present invention relates to a microwave oven equipped with an absolute humidity detection device that can operate normally even when starting from a low temperature atmosphere.

BACKGROUND ART It is known to use an absolute humidity sensor (hereinafter referred to as an A II sensor) as a sensing element in an automatic food finishing control device for a microwave oven. As shown in FIG. 1, the AH sensor 10 is composed of a closed type sensor 13 and an open type sensor 12, and a thermistor 13a is connected to two thermistors 13a through a wire 131 inside a closed container 13e filled with dry air. It is connected and supported between the terminals 13C and 13C. Furthermore, a thermistor 12a is connected to two terminals 12C and 12C through a wire 12b inside a container 12e that is open to the outside.
12C and supported. This thermistor 1
3a and 12a have the same characteristics. Further, in order to equalize the heat between the closed container 13e and the open container 12e, a heat equalizing tube 14 formed of a heat conductive member is provided for the containers 13e and 12e.
are concatenated. The AI-1 sensor thus formed is supported on the terminal block 11 and covered with a wire mesh 15 through which air can freely circulate, as shown in FIG.

The thermistor A I-I sensor measures absolute humidity using the difference in thermal conductivity between humid air and dry air, and the principle circuit for humidity measurement is shown in FIG. In Figure 3,
R1 is a temperature detection element corresponding to the open type sensor 12 provided with the ventilation hole 12d, and R2 is a temperature compensation element corresponding to the closed type sensor 13 sealed with dry air. ■ζ
is a constant voltage power supply, R3,■ (4 is a resistor that constitutes bridge circuit B, and Rs is a resistor connected in series to bridge circuit B. Resistor Rs functions to limit the magnitude of the flowing current, and this In the circuit, the resistance value is selected so that the temperature of the thermistor is approximately 200° C. due to Joule heat.

Now, a humidity sensor consisting of a resistor R1, 1<-2 is placed in an atmosphere of dry air, and the resistance value of the resistor R3, 4 is adjusted so that the output voltage (2) of the bridge circuit B becomes zero. Next, this sensor is placed in a humidity atmosphere and the relationship between its output V and absolute humidity is examined. An example of the absolute humidity-output characteristics measured in this way is shown in FIG. As is clear from FIG. 4, there is a nearly linear relationship between absolute humidity and the sensor output, and the absolute humidity can be directly read from the sensor output.

If we consider this qualitatively, the thermistor 12a is an AH sensor used in microwave ovens.

13a (Fig. 1) are both self-heated to 150 to 200°C by Joule heat, so the open type sensor 12
The thermistor 12a receives air containing water vapor (humid air) due to changes in humidity, and its thermal conductivity varies greatly depending on the amount of water vapor itself, compared to the thermistor 13a of the sealed sensor 13 containing dry air. In other words, the thermistor 12a exposed to humid air is cooled and the resistance value of 1 (1) increases, causing the bridge to become unbalanced.This imbalance causes an output that is linear and corresponds to the absolute humidity.

As shown in FIG. 5, the microwave oven using the above-mentioned AH sensor has a magnetron 6 and a heater 44 attached to the ceiling of the oven 5, and the food 7 placed on the cooking table 4 is exposed to the oscillation of the magnetron 6. heated by. Further, the inside of the oven 5 is heated by the heater 44. Food 7
The gas generated by the heating is passed through the exhaust passage 9 by the fan 8.
After that, it is discharged to the outside. The All sensor 10 is attached facing the exhaust passage 9 and detects the humidity of the gas passing through the exhaust passage 9. As shown in FIG. 6, the front surface of the microwave oven is provided with an operation panel 1, and on the operation panel 1 are provided a menu selection key 2 and a heating start button 1-3.

An example of a specific circuit configuration of a microwave oven using the above-mentioned AH sensor is shown in FIG. In FIG. 7, the same reference numbers as in FIG. 2, FIG. 3, FIG. 5, and FIG. 6 indicate the same or equivalent parts.

In FIG. 7, E is a DC constant voltage source, 16 is a DC amplifier, 17 is an A/I converter that converts the analog output of the DC amplifier 16 into a digital value, and 18 is an interface with a microcomputer or microprocessor 19. The interface circuit, microcomputer or microprocessor 19 includes a C'PU 19a, which is the main body for calculation and control, and a ROM 19b, which stores programs for calculation and control processing, a table database based on the table in FIG. 4, etc. and RAM 19c used for storing external programs, registers, flags, etc.

20 is a transistor that operates in response to the output of the microprocessor 19; 21 is a relay having a relay coil connected in series to the transistor 2o; its contacts are connected to a commercial power supply line 22 that supplies power to the magnetron 6;

In operation, first press the menu selection key on operation panel 1.
Press 2 and then press heating start key 3. The microprocessor 19 receives this start signal and outputs "Ilight" to the transistor 20 via the interface circuit 18.
"The level signal is transmitted and the relay 21 is turned on. Then, the magnetron 6 oscillates and the food is heated. At this time, the A1.1 sensor 10 installed in the exhaust passage 9
Detects water vapor emitted from food. A 14 sensor 1
The output voltage of 0 is passed through the bridge circuit B to the DC amplifier 1.
A/I) converter 17 converts the signal into a digital signal, which is then input to the microprocessor 19 via the interface circuit 18. The input data is C
The PUI 9H performs a point-by-point comparison with the optimality-1 yuri level value for each temperature previously stored in the technique OM1gb, and the operation of the magnetron 6 is continued until that level is reached. A lot of water vapor is generated from food, and AH sensor 1
0 detects its absolute amount and reaches the "optimality" level, the microprocessor 19 controls the interface circuit 18.
A "Low" level signal is applied to the transistor 20 through the transistor 20. The relay 21 is then deenergized and its contacts open.

Immediately, the oscillation of the magnetron 6 stops, and cooking heating is stopped. Heating stop control is generally performed as described in 6 above, but the details of the sensor output capture, sensor data processing in the microprocessor 19, etc. are already known and will not be described in detail.

The power supply to the A r-1 sensor of the microwave oven described above is performed by a DC power source E obtained by rectifying the commercial AC from the commercial power supply line 22, as shown in FIG. When the commercial power supply line 22 is connected to a commercial AC power source (not shown) when the microwave oven is used, power is supplied from the DC power source E to the AH sensor 10.

'Then, current flows through the A I-1 sensor 10, and the V-I of the thermistor shown in FIG.
The inflow current increases according to the characteristics, and the current limiting resistor R
With the current increasing to the value determined by s, A I
- ■ The sensor 10 self-heats.

As shown in Figure 9, the thermistor exhibits ohmic characteristics because the amount of self-heating is small while the power consumption is low, but as the current increases, the amount of self-heating increases and the resistance of the thermistor changes due to temperature rise. becomes large, and reaches the maximum voltage value at a certain current value. Then, as the power is further increased, the voltage decreases. A H sensor is this V
The operating point is determined so as to operate in a stable region with large self-heating to the right of the peak of the −I characteristic.

In addition, as shown in Figure 9, the thermistor's ■ - Atmosphere characteristics? It changes depending on the Rr degree, and as the ambient temperature decreases, the resistance increases and it becomes difficult for current to flow. Therefore, when the ambient temperature is low, unless the applied voltage is increased, the current flowing through the thermistor will not increase, and the thermistor will not reach the required temperature. As mentioned above, in the microwave oven, the →no-mistor is used by self-heating to 150 to 200°C, but since the ambient temperature is low, the thermistor resistance xt1 of the A ri sensor 10. Even if the commercial power supply line 22 is connected to a commercial power source and a DC voltage is applied to the thermistor with R2 having a high resistance, the temperature of the thermistor will not rise to 150 to 200 degrees Celsius because the current flowing through the thermistor is small. cause problems. Thermistor temperature is 150~
If the temperature does not reach 200°C, it will not be able to function as an AI-1 sensor.

In connection with this point, in a measuring instrument using a thermistor, the voltage applied to the thermistor is increased only during startup, and after the thermistor is warm-amplified, the voltage is lowered to the rated voltage. However, this case has the disadvantage of requiring a complicated circuit for warm-up.

Purpose The present invention has been made in view of the above circumstances, and its purpose is to heat A H by heating means when the ambient temperature is low.
To provide a microwave oven equipped with an absolute humidity detection device which heats the atmosphere of the sensor so that an AH sensor can operate normally even in a low temperature state.

Summary Forming an absolute humidity sensor when starting power supply 2
A signal corresponding to the ambient temperature of the thermistor obtained in a bridge circuit having two thermistors and two resistors on opposite sides of the thermistor and a predetermined base value of the temperature. When the ambient temperature of the thermistor is lower than the reference value, the ambient temperature of the thermistor is heated for a predetermined time or until the ambient temperature becomes higher than the reference value to promote self-heating of the thermistor.

Example An embodiment of the present invention will be described below.

FIG. 10 shows the circuit configuration of a microwave oven, in which a commercial power supply line 30 connected to a commercial AC power source (not shown) is connected to the primary side of a transformer 31, and rectified to the secondary side of the transformer 31. The AC side terminal of the circuit 32 is connected. A smoothing capacitor 33 is connected between the DC side output terminal 32a of the rectifier circuit 32 and the grounded terminal 32b. Furthermore, the input terminal 36 of the bridge circuit 36 is connected to the terminal 32a via the current limiting resistor 35.
A is connected. The other input terminal 3 of the bridge circuit 36
6b is grounded.

The bridge circuit 36 connects the thermistors 12a and 13a that constitute the AH sensor 10, and the thermistors 12a and 1
3a and resistors 38 and 39 on the opposite side. The thermistor 12a forms an open type sensor of the AH sensor 10, and the thermistor 13al;! AH sensor 1
0 to form a sealed sensor. This bridge circuit 36
The output terminal 36C936d of is connected to the input terminal of an amplifier 40, and the output terminal of this amplifier 40 is connected to the input terminal of an A-D converter 41 that converts an analog signal representing absolute humidity into a digital signal. The output terminal of this A-D converter 41 is connected to the interface circuit 18.

A magnetron control circuit 42 and a heater control circuit 43 are further connected to the interface circuit 18 .
The magnetron 6 for heating the food is turned on and off, and the heater control circuit 43 turns on and off the heater 44 for heating the oven (not shown).

This oven heating heater 44 is provided on the internal ceiling surface of the oven, and together with the oven, the above-mentioned AH sensor 1
It is arranged to heat an atmosphere of 0. A normally open contact 45 a is connected in parallel to a heater control circuit 43 interposed between the heater 44 and the commercial power supply line 30 that supplies power to the heater 44 . This normally open contact 45a is closed by excitation of a relay coil 45, which will be described later.

Between the output terminals 32a and 32b of the rectifier circuit 32,
A timer circuit 46 is connected. In this timer circuit 46, a resistor 47.4 is connected between the terminal 32a and the terminal 32b.
8 are connected in series, and a series circuit of a resistor 49 and a capacitor 50 is connected in parallel with this series circuit of resistors 47 and 48. Furthermore, the connection point of the resistors 47 and 48 is connected to the operational amplifier 51.
The connection point between the resistor 49 and the capacitor 50 is connected to the input terminal of the operational amplifier 51.

The output terminal 51a of this operational amplifier 51 is connected to the NAND circuit 52.
is connected to the first input terminal of.

A resistor 5 is connected between the output terminal 32a of the rectifier circuit 32 and the ground.
3 and a resistor 54 are connected in series, and this resistor 53.54
is connected to one input terminal of the comparator 55. The input terminal of the comparator 55 is connected to the output terminal 3 of the bridge circuit 36.
6d is connected, and the output terminal 55a of the comparator 55 is connected to the second input terminal of the NAND circuit 52. The output terminal of this NAND circuit 52 is connected to the input terminal of an inverter circuit 56, and the output terminal of the inverter circuit 56 is connected to the base of a transistor 57. Output terminal 3 of rectifier circuit 32
2a is further connected to one terminal of a relay coil 45, the other terminal of the relay coil 45 is connected to the collector of a transistor 57, and the emitter of this transistor 57 is grounded.

Next, the operation of the above circuit will be explained.

When the commercial power supply line 30 is connected to a commercial AC power supply and the heating start key 3 on the operation panel 1 on the front of the microwave oven is pressed, the magnetron control circuit 42 operates in response to a signal from the microprocessor 19, and the commercial power supply line 30 Power is supplied from the magnetron 6 to the magnetron 6.

The food is heated by the oscillation of the magnetron 6.

When the commercial power supply line 30 is connected to a commercial AC power source, the DC voltage output from the rectifier circuit 32 is connected to the bridge circuit 36.
is applied to The DC voltage from the rectifier circuit 32 is also applied to the timer circuit 46, and the reference voltage obtained by dividing the voltage with the resistors 47 and 48 is applied to one input terminal of the operational amplifier 51, and the time determined by the resistor 49 and the capacitor 50 is applied. A constant increasing voltage signal is applied to the ten input terminals of operational amplifier 51. While the voltage at the l input terminal of the operational amplifier 51 does not reach the reference voltage of the one input terminal after power supply is started, the output terminal 51a of the operational amplifier 51 becomes high" level. Then, after a certain period of time has elapsed, When the voltage at the 10th input terminal of the operational amplifier 51 reaches the reference voltage at the 1st input terminal,
The output terminal 51a of the operational amplifier 51 is inverted to "Low" level.

On the other hand, when power supply is started, due to the thermistor characteristics of the AH sensor 10, the output terminal 3 of the bridge circuit 36
At 6d, a signal corresponding to the ambient temperature of the AH sensor 10 is output. That is, since the AH sensor 10 is composed of a thermistor, as shown in FIG.
The terminal voltage of the AI-1 sensor, that is, the voltage of the output terminal 36d of the bridge circuit 36 changes depending on the ambient temperature of the HETO I sensor 10. Therefore, bridge circuit 3
The output voltage of the terminal 36d of No. 6 indicates the ambient temperature of the AH sensor 10.

A signal representing the ambient temperature of the AH sensor 10 is applied to the input terminal of the comparator 55. A signal representing a reference temperature value obtained by dividing the output voltage of the rectifier circuit 32 by resistors 53 and 54 is applied to one input terminal of the comparator 55. The reference value for this temperature is A
The temperature is set at around 5℃.

If the ambient temperature of the AH sensor 10 is lower than the reference value when power supply is started, the output terminal 5 of the comparator 55
5a becomes “High” level. At this time, the output terminal 51a of the operational amplifier 51 of the timer circuit 46 is "H".
Since the output of the NAND circuit 52 becomes "Low" level and the output of the inverter circuit 56 becomes "High" level, the transistor 57 becomes conductive.The conduction of the transistor 57 causes the relay coil 4 to become conductive.
5 is excited, contact 4-5a closes, current flows to heater 44, and the atmosphere of sensor 10 changes to this heater 44.
It is heated by applying electricity to it. A11 When the ambient temperature of the sensor 10 increases by 1, the curve of the V-I characteristic (Fig. 9) of the thermistor described above decreases, current flows through the thermistor more easily, self-heating of the thermistor is promoted, and V-
The stable region on the right side of the I-characteristic mountain is quickly reached. And A
When the ambient temperature of the sensor 10 rises and becomes higher than the reference temperature, the output terminal 551 of the comparator 55 becomes
ow” level.

Then, the output of the NAND circuit 52 becomes "High" level, the output power of the inverter circuit 56 becomes "Low" level, the transistor 57 is turned off, the relay coil 45 is de-energized, and the contact 45a is opened. heater 4
Power to 4 is stopped. Alternatively, after a certain period of time has passed since the start of power supply, the output terminal 51a of the operational amplifier 51 of the timer circuit 46 is inverted to "Low" level, and the NAND circuit 52
The output of is inverted to the "1 i gb" level, the transistor 57 is turned off, and the power supply to the heater 44 is stopped.

Since it takes several minutes for the thermistor to reach a stable range due to the heating of the atmosphere by the heater 44, the timer circuit 46 uses the output terminal 51 of the operational amplifier 51 for several minutes.
The time is set so that a becomes the "High" level.

On the other hand, if the ambient temperature of the AH sensor 10 is higher than the reference value when power supply is started, the output terminal 551 of the comparator 55 becomes <``Low'' level, and the output of the operational amplifier 51 of the timer circuit 46 Regardless of the state of the terminal 51a, the output of the NAND circuit 52 becomes "High" level, the output of the inverter circuit 56 becomes "Low" level, and the transistor 57 does not conduct. Therefore, the relay coil 45 is not excited and the contact 45a remains open and the heater 44 is not energized.In other words, when the ambient temperature around the AI-1 sensor 10 is high, the thermistor is sufficiently self-heated and can reach a stable range, so the heater 44 No heating of the atmosphere takes place.

Note that in the above-mentioned embodiment, the heater for open heating was also used to heat the atmosphere of the ATI sensor.
This can also be used as a magnetron for heating food. Further, a dedicated heater may be provided to heat the atmosphere of the AI-1 sensor.

Effect: Forms an absolute humidity sensor when power supply starts 2
A signal corresponding to the ambient temperature of the thermistor and a predetermined temperature reference value obtained in a bridge circuit having two thermistors and two resistors on opposite sides of the two thermistors. When the ambient temperature of the thermistor is lower than the reference value, the thermistor's atmosphere is heated for a predetermined time or until the ambient temperature becomes higher than the reference value to promote self-heating of the thermistor. Therefore, the absolute humidity sensor can be operated reliably, quickly, and stably even in a low-temperature atmosphere.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the All sensor, Figure 2 is a diagram showing the AH sensor assembled on the terminal block, Figure 3 is a circuit diagram showing the principle circuit of humidity measurement, and Figure 4 is absolute humidity - output. A graph showing the characteristics, Fig. 5 is a diagram showing the schematic configuration of a microwave oven using the A I-I sensor, Fig. 6 is a diagram showing the front configuration of the microwave oven, and Fig. 7 is a diagram showing the schematic configuration of the microwave oven using the A I-I sensor. Figure 8 is a circuit diagram showing the circuit configuration of a microwave oven.
9 is a graph showing the VI characteristic of the thermistor, FIG. 10 is a circuit diagram showing an embodiment of the present invention,
FIG. 11 is a graph showing the relationship between the output of the bridge circuit and the ambient temperature of the A I-I sensor. IQ---AH sensor, 12a, 13a-=thermistor, 30... commercial power supply line, 36... bridge circuit,
36d, 36C...Output terminal, 38.39...Resistor, 44...Heater, 45...Relay coil, 45a
...Contact, 46...Timer circuit, 52...NAND circuit, 53°54...Resistor, 55...Comparator, 56
...Inverter circuit, 57...Transistor. Patent applicant Sharp Co., Ltd. Representative Patent attorney Aoyama Sogai 2 people Figure 1 Figure 2 0 Figure 3 s Baninto - Jl 屓 (9/□・)

Claims (1)

[Claims] (1) A bridge circuit including two thermistors forming an absolute humidity sensor and two resistors on opposite sides of the two thermistors is provided, and a signal corresponding to the absolute humidity is generated at the output terminal of the bridge circuit. In a microwave oven equipped with an absolute humidity detection device configured to obtain an absolute humidity of a comparison means for comparing a signal corresponding to the ambient temperature of the thermistor with a signal corresponding to a predetermined temperature reference value; and when power supply is started, the ambient temperature of the thermistor is lower than the reference value. A microwave oven equipped with an absolute humidity detection device including a heating control means that energizes the heating means, sometimes for a time set in the timer or until the ambient temperature becomes higher than a reference value.